1. Field of the Invention
The present invention relates to a multistage transmission in which a plurality of drive gears and driven gears are rotatably supported by respective parallel gear shafts in a constant-mesh state for each speed-change stage.
2. Description of Background Art
This constant-mesh type multistage transmission is such that one of the drive gears and driven gears is secured to a gear shaft and the other is rotatably supported by the gear shaft and shifting is executed by switching a gear from the rotatable gears engaged with the gear shaft by engaging means.
The following configuration has previously been filed by the same applicant by way of example. In the configuration, a swing claw member operated by a cam member is used for engagement of the gear and the gear shaft (see Japanese Patent Application No. 2008-093702).
Engaging means of a multistage transmission disclosed Japanese Patent Application No. 2008-093702 is such that a swing claw member pivotally supported by a spindle pin provided on a gear shaft is designed to be biased in an engageable swing direction by a torsional coil spring wound around the spindle pin. In addition, a pin member abutted against a cam face of an axially sliding cam rod are advanced and retracted to swing the swing claw member to establish engagement and release the engagement.
Since the torsional coil spring is located close to the swing claw member and wound several times around the spindle pin, an axial space dedicated to the torsional coil spring is needed to enlarge the gear shaft in the axial direction.
The torsional coil spring is located close to one side of the swing claw member. In addition, a pin-receiving portion of the swing claw member adapted to receive the pin member abutted thereagainst is cut away and reduced in width at its one axial side and an engaging claw on the other side is increased in width to receive a centrifugal force largely acting thereon. Thus, the swing claw member is asymmetrical on both axial sides.
The swing claw members of two kinds in which the pin-receiving portion and the engaging claw member are arranged circumferentially oppositely to each other so as to establish engagement between the gear and the gear shaft and release the engagement in both the relative rotation directions thereof are provided on the gear shaft. However, the swing claw member per se is asymmetrical and the torsional coil spring is configured to be disposed close to one side of the swing claw member. Thus, the swing claw members of two kinds are shaped differently from each other. That is to say, the swing claw members having the same shape cannot be used.